The present invention relates to a camera with a liquid crystal aperture stop means.
In order to set a desired f-number, cameras have long used mechanical diaphragms or apertures comprising a plurality of thin metal leaves, but recently there has been devised and demonstrated electronically controlled liquid crystal aperture control or stop means which is based upon the principle that when an electric field is applied to a liquid crystal which is sandwiched between two sheets of glass, it becomes turbulent and scatters light. There have been also devised and demonstrated electronically controlled camera aperture control means which comprise polarizing plates and TN liquid crystals. The latter means have the advantages that the contrast ratio can be increased and the depth of field can be varied.
Liquid crystal aperture control means have the common advantages that their electronic controls can be facilitated and they can be easily combined with automatic control means, but they have also some defects. For instance, they cause the losses of quantity of light reaching the film. Light transmission losses are dependent upon the transmission coefficients of sheets of glass upon which are deposited transparent electrodes or polarizing plates which are used to enhance the transmission of light through the liquid crystal aperture control means. As compared with the mechanical aperture control means, the light transmission losses through the liquid crystal aperture control means are worse by about 10% or about 1 EV (exposure value) or one step in f-number. As a result, the distance at which an object can be satisfactorily exposed with the aid of a flash is decreased especially in cases of cameras with a built-in electronic flash device. To overcome this problem, compared with cameras with mechanical aperture control means, those with liquid crystal aperture control means must use large main flash capacitors if the same aperture is used.